On the Benefits of Pre-Equalization for ACO-OFDM and Flip-OFDM Indoor Wireless Optical Transmissions Over Dispersive Channels

Performance analysis of partial pre-equalization for ACO-OFDM indoor optical wireless transmissions

“…The even-numbered subcarriers are not used. A real OFDM signal can be obtained by applying the Hermitian symmetry property [7], [13] as follows.…”

“…Even though traditional downlink OFDM transmissions employ post-equalization by dividing the received signals by the subcarrier gains at the receiver, post-equalization can suffer from noise enhancement [6], [10]- [12]. In [13], pre-equalization is shown to help reduce the required transmit optical power for a given BER target in comparison to post-equalization for diffuse indoor OWC channels. In addition, while pre-equalization may affect the peak-to-average power ratio (PAPR) of OFDM signals, simulation results in [13] indicate that pre-equalization outperforms post-equalization in terms of the BER when transmitted signals are subject to signal clipping beyond a limited signal dynamic range at the transmitter.…”

“…In addition, it is not applicable for broadcasting to multiple receivers [10]- [13]. Partial preequalization is therefore proposed in this paper to overcome these limitations of pre-equalization.…”

Efficient OFDM transceiver design for VLC sys-tems in fading channel

“…VLC can support illumination and communication simultaneously and offers the benefits of high rates, low cost, safety, security, and no electronic interference. Therefore, VLC has been regarded as an important supplement to, or replacement of, traditional RF communication in indoor environments [5]- [8].To fulfill high-speed transmissions, orthogonal frequency-division multiplexing (OFDM),which has been widely used in 4G systems (e.g., LTE), has also been considered in VLC . However OFDM symbols are bipolar.…”

“…Several techniques are available to convert bipolar OFDM to unipolar. They are DC biased optical OFDM (DCO-OFDM), PAM-modulated discrete multitone (PAM-DMT), Asymmetrically Clipped optical OFDM (ACO-OFDM) [1] - [3], [5]. Most popular among them are ACO-OFDM and DCO-OFDM.…”